The present invention relates to a dual module magnetic record/reproduce head assembly, in particular to such an assembly that is capable of a read while write (RWW) operation, and to a technique for constructing such a head assembly.
The subject matter discussed herein generally relates to magnetic tape drives and, more particularly, to a magnetic tape head and techniques for assembly thereof, wherein the tape head assembly has multiple transducer heads which together form a predetermined overall contour, for multi-channel, high speed read-while-write type recording. As a general matter, a magnetic tape drive includes a head assembly, which carries at least a pair of transducers for reading information from and writing information to a magnetic tape as the tape passes over the assembly. The head assembly is positioned between a pair of guide rollers, which guide the tape over the head assembly. The head assembly is offset from the guide rollers during operations, to cause the tape to wrap onto the head.
Modern magnetic tape recorders utilize a read while write (RWW) capability to store data on the tape and to confirm that the writing of data was error free. A read-while-writing head assembly includes a write head in-line with a contiguous read head. The gap of the read head is closely spaced to the gap of the write head, with the read head positioned downstream of the write head in the direction of tape motion during the writing operation. The recorder continually reads xe2x80x9cjust recordedxe2x80x9d data throughout the write operation, to check correctness of the data at a time while the original data is still available in temporary storage in the recording system. The xe2x80x9cjust recordedxe2x80x9d data is read and checked against the original data, and appropriate action is taken upon detection of error. Many modern tape systems also support bi-directional writing to the tape. As such, the systems require that the head elements support the RWW operation for both directions of tape travel.
The heads in these assemblies are carefully contoured to achieve desired degrees of wrapping of the tape around the head assembly, as the tape contacts and passes over the head assembly. The transducers are fabricated on a ferrite or other ceramic substrate using thin film wafer technology.
For example, U.S. Pat. No. 5,034,838 to Brock et al. discloses a bi-directional magnetic head assembly consisting of two write heads arranged on opposite sides of one read head, along the line of bi-directional movement of the tape. Each inductive write head consists of two abutting segments of a refractory non-magnetic material, with a gap line formed along the abutment (perpendicular to tape travel). The magnetoresistive read head consists of two half sections with magnetoresistive transducing elements located in the gap between those sections. In this assembly, the central read head is curved and has slots on either side of its transducing region for skiving of entrained air and debris from the tape before the tape engages the transducing elements of the read head from either direction of tape travel. Each write head has a single slot outboard of the respective transducing gap for skiving entrained air and debris.
U.S. Pat. No. 5,953,184 to Barber et al. discloses a three-head assembly with a common surface contour. The assembly from this Patent includes an interior tape head module having a magnetic gap for the thin film transducers, with transverse slots on each side of the gap to eliminate air and debris as the tape moves in either direction over the module. The assembly also includes two exterior tape head modules, one on each side of the interior module. Each exterior module has a magnetic gap containing the appropriate thin film transducer elements and transverse slots on each side of the gap.
U.S. Pat. No. 5,237,476 to Bischoff et al. discloses a technique for forming a thin film tape head assembly. The patented method involves depositing thin film transducers on a ceramic wafer or substrate, which is then divided into head bars. Each head bar has one or more of the thin film transducers on its face. End sections and a cover bar are joined to the head bar to form a head bar subassembly. A flexible cable or electrical pins between the end sections enable electrical connection between the transducers in the head and external circuitry. The patent also suggests joining a number of these head bar subassemblies in parallel (perpendicular to the travel of the tape), to form a multigap thin film tape head for multiple read/write operations.
The trends in development of magnetic tape drives involve ever-increasing demands for the density of data stored on the tape as well as ever-increasing requirements for speed. With these trends, it is reasonable to expect that the tape head assembly must be re-designed if it can not function adequately at newly required higher speeds and/or higher densities. To avoid the need to re-design the tape head, particularly the contour thereof, there is a need for a tape head assembly that can operate properly at current speeds and can reasonably be expected to continue to function properly at higher speeds in next-generation tape drives. Stated another way, it is desirable for a tape head assembly to operate over a wide range of tape speeds.
As shown by the cited examples, there have been many different designs for the tape heads of digital data storage type tape drives. In some applications, it may be acceptable to dispose of the tape drive and thus the head after a working life of about three years. However, there are applications where the life expectancy of the drive is projected to be much longer, hence there is a need for a head assembly design that has low wear during protracted use and therefore a long life expectancy.
Another trend relates to expectations of decreasing costs. The costs of computer equipment and other electronic devices have continually spiraled downward for almost two decades. To continue to meet the demand for ever better tape drives at ever lower costs, there is a need for a design of a tape head assembly and an attendant manufacturing technique that reduces costs yet yields a high percentage of products with increased performance capabilities.
The use of a tape head assembly in a cartridge type system, particularly for a single real tape cartridge drive also imposes certain special requirements on the tape head. For example, in the single real design, there is a substantial difference in tension on the tape between initial withdrawal of tape from the reel and that required near the end of the tape. As a result, the head assembly must function properly over a wide range of tape tensions, with attendant differences in wrap and contact pressure.
A tape head assembly also should have a relatively high tolerance to differences in wrap angle of the tape about the assembly. To maintain a tight angle tolerance, the components of the drive must be built to very tight tolerances making the drive excessively expensive. If the wrap angle tolerance is relatively wide, the tolerances of other drive components are not as strict, and those components can be manufactured using less expensive techniques.
The inventive concepts meet the above noted needs for the structure and assembly of heads for read-while-writing (RWW) type magnetic tape systems. A tape head assembly, in accord with the aspects of the present invention, comprises two modules bonded together, for example, in a back-to-back arrangement. However, the initial phase of the manufacturing technique produces a single unit containing elements of both modules, for example, in a head-face to head-face arrangement. Transducer elements for both modules may be formed initially on different halves of a single substrate that is common to both modules.
The modules are initially gapped in pair, in order to produce a good reference surface, which insures that the head will meet tight azimuth and gap distance tolerances in a low cost assembly process. The unit is then machined to separate the modules, essentially to cut the integral unit into two halves forming the individual modules. The inventive assembly technique then entails individually machining the head surface of each separate module, to achieve desired contours. Each module may be separately tested before final assembly. The machined modules are then brought together in the positional arrangement required to form the final head assembly.
Hence, one aspect of the invention relates to a magnetic tape head assembly, for use with a magnetic recording tape passing thereover. The assembly includes at least two transducers. One of the transducers is for writing data to the magnetic tape, and the other transducers is for reading data from the tape during a read-while-writing operation, for example, as the tape travels in one direction over the assembly. In preferred embodiments, if the tape travels in the opposite direction, the functions of the two transducers are reversed. As such, the assembly preferably supports bi-directional operation. The assembly also includes means for mounting the transducers to form a composite assembly of two head modules. These means also provide a predetermined working contour for the assembly, enabling high-speed and high-density read-while-writing operation.
In disclosed embodiments, the contour enables the assembly to skive air and debris off a surface of the tape before passage of the tape over the transducers. The contour allows the tape to fly over a portion of the contour, and facilitates contact of the tape to a region of the contour including transducers with a low constant contact pressure during the read-while-writing operation.
A preferred embodiment of the assembly comprises a first module and a second module attached to each other, for example, in a back-to-back arrangement. Each module comprises an element chip, having one or more thin film transducer elements. In each module, a cover bar is bonded to an outer or front surface of the element chip. The tape facing surfaces of the modules are machined to have mirror-image contours, such that when the inner or back surfaces of the units are bonded together (to achieve the back-to-back arrangement), the mirror-image contours of the two modules form a substantially contiguous working contour for the assembly.
In this assembly, each working contour comprises an element bump around the respective transducer elements, a pair of grooves on opposite sides of the element bump, and a pair of outriggers. In a preferred embodiment, the contour also includes a central notch around the bound line between the two modules. Portions of the tape facing surfaces of the wafer chips and the cover bars are machined to a common radius of curvature on each module. In the preferred embodiment, the radial dimension is the same, although when assembled, the arcs have different center points.
Another aspect of the invention relates to a method for constructing a magnetic tape head assembly. This inventive method involves forming a pair of transducer elements on a common thin film tape head wafer chip and attaching the thin film tape head wafer chip to a double-width cover bar to form an intermediate assembly. The intermediate assembly is cut in two, to form two separate modules, each of which includes a chip containing one set of transducers and a cover bar. The formation of two modules in one integral intermediate assembly increases manufacturing speed and makes the components, which are larger, easier to handle. Also, the surface of the cover bar serves as a reference surface, insuring that the opposing surface(s) of the resulting module are substantially planar.
The inventive method then entails machining tape facing surfaces of the semiconductor wafer chip and the cover bar, of each of the separate modules. This machining step produces separate mirror-image working contours on the two modules. Each separate working contour comprises an element bump, grooves on opposing sides of the element bump, and an outrigger adjacent to each groove. Two modules, formed and machined in this fashion, are then bonded together in back-to-back relation. In this arrangement, the mirror-image working contours together form a substantially contiguous working contour for the head assembly.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following and the accompanying drawings or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.